Arsenate Uncoupling of Oxidative Phosphorylation in Isolated Plant Mitochondria

Abstract

The uncoupling by arsenate of beetroot and cauliflower bud mitochondria showed the following characteristics: (1) arsenate stimulation of respiration above the rate found with phosphate; (2) inhibition of arsenate-stimulated respiration by phosphate; (3) enhancement of arsenate-stimulated respiration by ADP; (4) only partial prevention of this ADP-enhanced respiration by atractyloside; (5) inhibition by oligomycin of the arsenate-stimulated respiration back to the phosphate rate; and (6) the absence of any stimulatory effect of ADP in the presence of oligomycin. These results are qualitatively analogous to those reported for arsenate uncoupling in rat liver mitochondria. Arsenate stimulated malate oxidation, presumably by stimulating malate entry, in both beetroot and cauliflower bud mitochondria; however, high rates of oxidation, and presumably entry, were only sustained with arsenate in beetroot mitochondria. NADH was oxidized rapidly in cauliflower bud mitochondria in the presence of arsenate, showing that arsenate did not inhibit electron transfer processes.